The invention relates to a method for joining tubing, fittings and valves of different standard diameter types.
For the purposes of the invention description presented herein, "CT" will be used to represent "standard water tube" size copper and copper alloy tubing, and "IP" will be used to represent "standard outside diameter" size steel pipe. In addition, the terms "tubing" and "pipe" are considered to be interchangeable, and reference to "copper tubing" will also be taken as referring to "copper alloy tubing" as an alternative.
A grooved end pipe coupling, e.g. of the type illustrated in FIGS. 1 and 1A, is used for joining together piping elements, e.g. tubing, fittings, valves, etc., in a leak tight assembly by use of grooves that are cut, cast or formed in the ends of the piping elements. Referring to FIGS. 2 and 3, critical parameters of a grooved end connection include: the gasket seat diameter, D.sub.s, groove diameter, D.sub.g, gasket seat width, W.sub.s, and groove width, W.sub.g. In the case of wrought metal piping elements, e.g., as above, tubing, fittings or valve bodies, the grooved end of the piping element, P, is conventionally produced by either a cut (machining) operation or a rolling (contour roll forming) operation as shown in piping element, P.sub.cut, of FIG. 2, and piping element P.sub.roll, of FIG. 3, respectively. In the case of a cast fitting or valve body, the grooved end connection is normally either cut in the configuration of a piping element, P.sub.cut shown in FIG. 2, or cast in the dual outward step configuration of a piping element, P.sub.cast, shown in FIG. 4.
Cut grooves for use with grooved end pipe couplings are typically prepared by the use of a lathe and, heretofore, roll grooves for use with grooved end pipe couplings have been prepared by an apparatus similar in function to that described in Kunsman, U.S. Pat. No. 3,995,466 and Dole, U.S. Pat. No. 5,279,143. Both of these patents describe a means for contour roll forming a groove in the end of the pipe element by which a segment of the pipe is press formed or stretched into the desired configuration by forcing a shaped die roll located outside of the pipe against a form roll located inside of the pipe.
Other examples of contour roll forming of pipes are presented in Constantine, Great Britain Patent 18201, Pritchett et al., U.S. Pat. No. 3,191,416 and Vaill et al., U.S. Pat. No. 3,290,914. Although these letter three patent references describe devices which force a die roll located inside the pipe against a form located outside of the pipe, the contour roll forming principle is the same as for the previous two patent references. That is, the pipe is locally shaped by radial press forming or stretching, into the desired contour.
Referring again to FIGS. 1 and 1A, a typical grooved end pipe coupling 10 consists of two or more housing segments 12, 14, a gasket 16, and fastening means, e.g. nuts 18 and bolts 20 for securing the assembly together with the end connections to be joined. The housing segments have keys 22 around the inner periphery at both ends, a shoulder 24 also around and just inside of each key, and a gasket cavity 26. The keys fit into the grooves 30 to axially and transversely retain the end connections. The keys and shoulders are involved to varying degrees in maintaining the coupling assembly generally centered about the grooved end connection. The shoulder fits closely around the gasket seat diameter to prevent the gasket from extruding outwardly under the internal pressure of the piping system, the gasket being retained in the gasket cavity and producing a seal on the gasket seat surfaces to form a leak tight assembly.
Traditionally, copper tubing has been joined by soldering or brazing. However, recent emphasis on use of lead free solder has considerably increased the difficulty of producing a soldered, leak free joint, especially in the 3 inch and above tubing diameter sizes. This has increased the potential cost effectiveness of using grooved end pipe couplings in copper tubing system construction.
Until now, grooved end pipe couplings for joining copper piping elements (tubing, fittings, valves, etc.) have only been available in couplings specifically designed to accommodate roll grooved (contour roll formed) CT size wrought copper tubing, which has average outside diameters that are slightly less than those for the same nominal IP size steel pipe (as detailed, e.g., in the publication "The Copper Connection" by The Victaulic Company of America). By way of example only, a 4-inch nominal CT size copper tube has an average outside diameter ("OD") of 4.125 inches, while 4-inch nominal IP size steel pipe has an average outside diameter of 4.500 inches.
In addition to the use of specifically designed grooved end pipe couplings, however, within the present state of the art, other means have been employed to join tubing with an average outside diameter smaller than the actual diameter of an IP size steel pipe of the same nominal diameter. For example, a specially designed ring with an average outside diameter equivalent to that of IP size pipe may be secured in a sealed arrangement to the end of a tube having a smaller average outside diameter, or the average outside diameter of the pipe can be increased to that of IP size pipe through the use of a ring secured in a sealed arrangement around the ends of lower average diameter pipe. These approaches would be similar to the Type A through E pipe end ring concepts shown in AWWA Standard C-606 for Grooved and Shouldered Joints.
Also, within the grooved end pipe coupling industry, it has been known to expand the end of a pipe by contour roll forming although the published objectives of this concept have been to either expand the ends of IP size grooved end steel pipe to eliminate the reduced wall thickness of cut (machined) groove joints, or to eliminate the protrusion 32 inside the pipe which is associated with conventional roll grooving as shown in FIG. 3, and described in Table A, below.
TABLE A ______________________________________ Roll Groove Dimensions for Steel Pipe (Inches) NOMINAL W.sub.S W.sub.g D.sub.g D.sub.s ______________________________________ 2 .625 .344 2.250-.015 2.375 21/2 .625 .344 2.720-.018 2.875 3 .625 .344 3.344-.018 3.500 4 .625 .344 4.344-.020 4.500 5 .625 .344 5.395-.022 5.562 6 .625 .344 6.455-.022 6.625 Tolerances: W.sub.s, W.sub.g = .+-..030 D.sub.g = +.000 D.sub.s = See IP size OD tolerances in TABLE I (below). ______________________________________
Prior art concerning roll grooving (contour roll forming) of copper tubing is also described in the brochure "The Copper Connection", by Victaulic Company of America, with respect to their specially designed copper connections. These grooved end couplings are of the same basic concept or design as grooved end pipe couplings for roll grooved IP size steel pipe; however, the dimensions of the couplings have been dimensionally altered to accommodate the smaller average outside diameter dimensions for copper tubing.
Standard roll grooving reduces the internal diameter of the tubing at the roll groove and thereby increases the restriction to the fluid flow stream. This somewhat impedes fluid flow through the pipe and also creates a more pronounced area for possible damage when used in abrasive media service. This factor is described in literature for the Victaulic Company of America Style 24 expanded pipe coupling, which is used to expand carbon steel pipe in abrasive service where the radially inward indentation created by standard roll grooving would be subject to excessive abrasion. This process, however, forms only the pipe end shoulder (gasket seating surface).